The present invention relates to polyhydroxyalkanoate copolymer (PHA) compositions having short annealing cycle times for manufacturing molded or extruded articles such as, for example, disposable articles, in particular, tampon applicators. Such molded or extruded articles are readily environmentally degradable.
Polyhydroxyalkanoates (PHAs) are thermoplastic polymers desirable for use in molded or extruded articles particularly due to their biodegradability. However, existing PHA copolymer compositions are slow to crystallize and producing molded or extruded articles therefrom remains nonviable commercially. It is necessary for compositions to solidify in a mold in as short a cycle time as possible to allow a manufacturing process to be economically feasible.
U.S. Pat. No. 5,498,692, issued Mar. 12, 1996 to Noda, and U.S. Pat. No. 5,502,116, issued Mar. 26, 1996 to Noda, relate to molded articles comprising PHAs. Molded articles from such PHAs remain substantially tacky after they are cooled down from the melt, and remain as such until sufficient crystallinity sets in, particularly with PHA copolymers levels above 10 wt %. Residual tack typically can lead to material sticking to itself or to the processing equipment, or both, and thereby can restrict the speed at which a polymeric product is produced or prevent the product from being collected in a form of suitable quality. A poly(3-hydroxybutyrate-co-3-hydroxyvalerate) product commercialized under the name BIOPOL(copyright) suffers from hardness, brittleness, and from having very slow crystallization kinetics. Similarly, U.S. Pat. No. 5,292,860 to Shiotani lacks teachings regarding compositions having short cycle times in the manufacturing process for molded or extruded articles.
Consequently, there is a need for melt processable compositions of PHAs having economically viable annealing cycle times for use in molded or extruded articles. Moreover, the compositions should be suitable for use in conventional processing equipment, be environmentally degradable, and meet consumer acceptability for their structural integrity and aesthetic characteristics of smoothness, flexibility, reduced stickiness, stability, and the like.
Molded or extruded articles of the present invention comprise a PHA copolymer having at least two randomly repeating monomer units (RRMUs)
wherein a first monomer unit has structure (I) 
where R1 is CH3, and n is 1; and
wherein a second monomer unit has structure (II) 
where R2 is CH2CH2CH3.
Such a PHA is referred to herein as a C4C6 PHA copolymer. For the present invention, between 2 and 8% of the randomly repeating monomer units has the structure of the second monomer unit, the C6 unit. Further, such compositions are demonstrated herein to provide an annealing cycle time that is at least ten seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8% or greater than 8% of the randomly repeating monomer units have the structure of the second monomer unit. In certain embodiments of the invention, such an annealing cycle time is at least 15, 20, 25, 30, 35, 40, 45, or 50 seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8% or greater than 8% of the randomly repeating monomer units have the structure of the second monomer unit. A process of forming a molded or extruded article comprises heating to a molten state a C4C6 PHA copolymer as described herein, allowing the melted blend to anneal; and molding or extruding the article, the process having an annealing cycle time that is at least ten seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8% or greater than 8% of the randomly repeating monomer units have the structure of the second monomer unit.
The present invention also provides flushable tampon applicators comprising such PHA compositions wherein the applicator is greater than 50% disintegrated within 28 days under anaerobic conditions.
Filed on an even date herewith is U.S. Pat. Ser. No. 10/431,796, of the present inventors to PHA compositions in blends with an environmentally degradable polymer wherein molded or extruded articles made therefrom also provide annealing cycle times that are commercially feasible.
As used herein, a xe2x80x9cmolded or extruded articlexe2x80x9d is an object that is formed from a PHA copolymer as set forth herein using molding or extrusion techniques such as injection molding, blow molding, compression molding, or extrusion of pipes, tubes, profiles, cables, or films. Molded or extruded articles may be solid objects such as, for example, toys, or hollow objects such as, for example, bottles, containers, tampon applicators, applicators for insertion of medications into bodily orifices, medical equipment for single use, surgical equipment, or the like.
The annealing cycle time is defined herein as holding time plus cooling time. With process conditions substantially optimized for a particular mold, an annealing cycle time is a function of copolymer composition. Process conditions substantially optimized are the temperature settings of the zones, nozzle, and mold of the molding apparatus, the shot size, the injection pressure, and the hold pressure. Annealing cycle times provided herein are at least ten seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8%, or greater than 8%, of the randomly repeating monomer units have the structure of the second monomer unit. In certain embodiments of the invention, the annealing cycle time for a molded or extruded article is at least 15, 20, 25, 30, 35, 40, 45, or 50 seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8% or greater than 8% of the randomly repeating monomer units have the structure of the second monomer unit. A dogbone tensile bar having dimensions of xc2xd inch length (L) (12.7 mm)xc3x97xe2x85x9 inch width (W) (3.175 mm)xc3x97{fraction (1/16)} inch height (H) (1.5875 mm) made using an Engel Tiebarless ES 60 TL injection molding machine as provided herein provides a standard article as representative of a molded or extruded article for measuring annealing cycle times herein.
The holding time is the length of time that a part is held under a holding pressure after initial material injection. The result is that air bubbles and/or sink marks, preferably both, are not visually observable on the exterior surface, preferably both exterior and interior surfaces (if applicable), with the naked eye (of a person with 20xe2x80x9420 vision and no vision defects) from a distance of about 20 cm from the surface of the molded or extruded article. This is to ensure the accuracy and cosmetic quality of the part. Shrinkage is taken into account by the mold design, however, shrinkage of about 1.5% to 5%, from about 1.0% to 2.5%, or 1.2% to 2.0% may occur. A shorter holding time is determined by reducing the holding time until parts do not pass the visual test described supra, do not conform to the shape and texture of the mold, are not completely filled, or exhibit excessive shrinkage. The length of time prior to the time at which such events occur is then recorded as a shorter holding time.
The cooling time is defined as the time for the part to become solidified in the mold and to be ejected readily from the mold. The mold includes at least two parts, so that the molded article is readily removed. For removal, the mold is opened at the parting line of the two parts. The finished molded part can be removed manually from the opened mold, or it can be pushed out automatically without human intervention by an ejector system as the mold is being opened. Depending on the part geometry, such ejectors may consist of pins or rings, embedded in the mold, that can be pushed forward when the mold is open. For example, the mold can contain standard dial-type or mechanical rod-type ejector pins to mechanically assist in the ejection of the molded parts. Suitable size rod-type ejector pins are xe2x85x9xe2x80x3 (3.175 mm), and the like. A shorter cooling time is determined by reducing the cooling time until parts become hung up on the mold and cannot readily pop out. The length of time prior to the time at which the part becomes hung up is then recorded as a shorter cooling time.
Processing temperatures that are set low enough to avoid thermal degradation of the polymer material, yet high enough to allow free flow of the material for molding are used The PHA copolymer is melt processed at melting temperatures less than about 180xc2x0 C. or, more typically, less than about 160xc2x0 C. to minimize thermal degradation. In general, polymers can thermally degrade when exposed to temperatures above the degradation temperature after melt for a period of time. As is understood by those skilled in the art in light of the present disclosure, the particular time required to cause thermal degradation will depend upon the particular material, the length of time above the melt temperature (Tm), and the number of degrees above the Tm. The temperatures can be as low as reasonably possible to allow free-flow of the polymer melt in order to minimize risk of thermal degradation. During extrusion, high shear in the extruder increases the temperature in the extruder higher than the set temperature. Therefore, the set temperatures may be lower than the melt temperature of the material. Low processing temperatures also help to reduce cycle time. For example, without limitation, the set temperature of the nozzle and barrel components of the injection molding machine can vary according to the melt processing temperature of the polymeric material and the type of molds used and can be from about 20xc2x0 C. degrees below the Tm to about 30xc2x0 C. above the Tm, but will typically be in the following ranges: nozzle, 120-170xc2x0 C.; front zone, 100-160xc2x0 C.; center zone, 100-160xc2x0 C.; zone, 60-160xc2x0 C. The set mold temperature of the injection molding machine is also dependent on the type of polymeric material and the type of molds used. A higher mold temperature helps polymers crystallize faster and reduces the cycle time. However, if the mold temperature is too high, the parts may come out of the mold deformed. The mold temperature is 5-60xc2x0 C. Typically, the mold temperature is 25-50xc2x0 C.
Molding injection speed is dependent on the flow rate of the compositions. The higher flow rate, the lower viscosity, the lower speed is needed for the injection molding. Injection speed can range from about 5 cm/sec to 20 cm/sec, in one embodiment, the injection speed is 10 cm/sec. If the viscosity is high, the injection speed is increased so that extruder pressure pushes the melt materials into the mold to fill the mold. The injection molding pressure is dependent on the processing temperature and shot size. Free flow is dependent upon the injection pressure reading not higher than about 14 Mpa.
To obtain the annealing cycle times for manufacturing molded or extruded articles of the present invention, between 2 and 8 mole percent of the PHA copolymer comprises RRMUs having the structure of the second RRMU of structure (II). Suitably, the molar ratio of the first RRMU to the second RRMU in the copolymer is in the range between 98:2 to 92:8. In further embodiments, the molar ratio is in the range of from about 97.5:2.5 to about 92.5:7.5, 97:3 to about 93:7, 96.5:3.5 to about 93.5:6.5 or from about 96:4 to about 94:6. In addition, the polyhydroxyalkanoate copolymer suitably has a number average molecular weight of greater than about 50,000 g/mole, greater than 150,000 g/mole or, in a further embodiment, greater than 250,000 g/mole.
The C4C6 polyhydroxyalkanoate copolymers set forth herein can be synthesized by chemical or biological methods as disclosed, for example, by Noda in U.S. Pat. No. 5,990,271, Noda, et al. in U.S. Pat. No. 5,942,597, both of which are incorporated herein by reference, Fukui, T. and Doi, Y. Appl. Microbiol. Biotechnol, 49:333-336 (1998), and Kichise, T. et al. Int""l. J. of Biological Macromolecules, 25:69-77 (1999). The amount of C6 in the final product is determined by standard methods such as NMR or GC MS methods such as described in Doi, Y. et al., Macromolecules 28, 4822 (1995) and Fukui, T. et al., Biomacromolecules 3, 618 (2002).
In molded or extruded articles of the present invention, C4C6 PHAs having 2%-8% C6 comprise 300% to 100%, 40% to 90% or, in a further embodiment of the invention, 50% to 85% weight percent of the molded or extruded article.
Optional materials may be used as processing aids to modify the processability and/or to modify physical properties such as elasticity, tensile strength and modulus of the final product. Other benefits include, but are not limited to, stability including oxidative stability, brightness, color, flexibility, resiliency, workability, processing aids, viscosity modifiers, and odor control. These optional ingredients may be present in quantities of less than about 70%, from about 0.1% to about 50%, from about 0.1% to about 40% or, in another embodiment, from about 0.1% to about 20% by weight of the composition.
Plasticizers may be used in the composition to modify the mechanical properties of products formed from the composition. In general, a plasticizer tends to lower the modulus and tensile strength, and to increase the ultimate tensile elongation, impact strength, and tear strength of the polymeric product. The plasticizer may also be used to lower the melting point of the composition to thereby enable melt-processing at lower temperatures and to minimize energy requirements and thermal degradation. These plasticizers are typically not required in order to obtain the advantageous combination of properties discussed above.
Nonlimiting examples of plasticizers include hydroxyl plasticizers, sugar alcohols, polyols, hydrogen bond forming organic compounds which do not have hydroxyl group, including urea and urea derivatives, anhydrides of sugar alcohols, animal proteins, vegetable proteins, organic acid esters which are biodegradable, aliphatic acids, or the like. Suitable plasticizers are exemplified by glycerol triacetate, methyl ricinolate, dimethyl sebacate, dihexyl phthalate, caprolactone diol, caprolactone triol, and others such as those described in the above referenced U.S. Pat. Nos. 3,182,036 and 5,231,148.
In further embodiments, a plasticizer is selected from the group consisting of dimethyl sebacate, glycerin, triacetin, glycerol, monostearate, sorbitol, erythritol, glucidol, mannitol, sucrose, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, diethylene glycol dibenzoate, dipropylene glycol dibenzoate, triethylene glycol caprate-caprylate, butylene glycol, pentamethylene glycol, hexamethylene glycol, diisobutyl adipate, oleic amide, erucic amide, palmitic amide, dimethyl acetamide, dimethyl sulfoxide, methyl pyrrolidone, tetramethylene sulfone, oxa monoacids, oxa diacids, polyoxa diacids, diglycolic acids, triethyl citrate, acetyl triethyl citrate, tri-n-butyl citrate, acetyl tri-n-butyl citrate, acetyl tri-n-hexyl citrate, alkyl lactates, phthalate polyesters, adipate polyesters, glutate polyesters, diisononyl phthalate, diisodecyl phthalate, dihexyl phthalate, alkyl alylether diester adipate, dibutoxyethoxyethyl adipate, and mixtures thereof. Suitable molecular weights are less than about 20,000 g/mol, less than about 5,000 g/mol or, in a further embodiment, less than about 1,000 g/mol. If present, the amount of plasticizer in the final molded or extruded article composition is from about 0.1% to about 70%, from about 0.5% to about 50% or, in a further embodiment, from about 1% to about 30%.
Nucleating agents are generally used to increase the crystallization rate, reduce the size of crystals, and improve transparency. Nucleating agents can also improve the meltflow and demolding behavior of partly crystalline plastic materials such as thermoplastic polyesters. A second polyhydroxyalkanoate such as polyhydroxybutyrate can act as a nucleating agent for the first polyhydroxyalkanoate and thereby improve the crystallization rate of the first polyhydroxyalkanoate such as disclosed by Autran, et al. WO02/055581 and WO02/50156, each filed Dec. 20, 2001. Further nucleating agents include talc, boron nitride, titanium oxide, micromica, chalk, salts, sorbitol acetal, clay, calcium carbonate, sodium chloride, calcium phosphate, LICOMONT(copyright) CaV 102 and LICOMONT(copyright) NaV 101 (the calcium and sodium salt, respectively, of montanic acid, i.e., long chain (C28-C32) linear carboxylic acids) both of which are commercially available from the Clariant Corporation (Coventry, R.I.); and MILLAD(copyright) 3988 (1,2,3,4-bis-3,4-dimethylbenzylidene sorbitol) which is commercially available from Milliken Chemical (Inman, S.C.). Nucleating agents commonly constitute from about 0.01% to about 5% of the weight of the molded or extruded articles, when used.
Further optional ingredients include salts, slip agents, crystallization accelerators or retarders, odor masking agents, cross-linking agents, emulsifiers, surfactants, cyclodextrins, lubricants, other processing aids, optical brighteners, antioxidants, flame retardants, dyes, pigments, fillers, proteins and their alkali salts, waxes, tackifying resins, extenders, chitin, chitosan, and mixtures thereof.
A filler may further be selected from the group of clays, silica, mica, wollastonite, calcium hydroxide, calcium carbonate, sodium carbonate, magnesium carbonate, barium sulfate, magnesium sulfate, kaolin, calcium oxide, magnesium oxide, aluminum hydroxide, talc, titanium dioxide, wood flour, walnut shell flour, alpha cellulose floc, cellulose fibers, chitin, chitosan powders, organosilicone powders, nylon powders, polyester powders, polypropylene powders, starches, and mixtures thereof. When present, the amount of fillers is from 0.1% to 60% by weight of the molded or extruded articles.
A lubricant may, for example, be selected from the group consisting of metal soaps, hydrocarbon waxes, fatty acids, long-chain alcohols, fatty acid esters, fatty acid amides, silicones, fluorochemicals, acrylics, and mixtures thereof. When present, the amount of lubricants is from 0.1% to 20% by weight of the molded or extruded articles.
Other polymers, such as non-degradable polymers, may also be used in the present invention depending upon final use of the molded or extruded article, processing, and degradation or flushability required. Commonly used thermoplastic polymers include polypropylene and copolymers thereof, polyethylene and copolymers thereof, polyamides and copolymers thereof, polyesters and copolymers thereof, and mixtures thereof. When present, the amount of non-degradable polymers is from about 0.1% to about 40% by weight of the molded or extruded articles.
Natural polymers may also be used in the present invention. Starch or a protein-based polymer can be used. Suitable starches include corn starch, potato starch, sweet potato starch, wheat starch, sago palm starch, tapioca starch, rice starch, soybean starch, arrow root starch, bracken starch, lotus starch, cassava starch, waxy maize starch, high amylose corn starch, and commercial amylose powder. Blends of starch may also be used. The starch should be destructurized. Suitable protein-based polymers include soy protein, zein protein, and combinations thereof. The natural polymer may be present in an amount of from about 0.1% to about 80% or, in a further embodiment, from about 1% to about 60%.
Molding and extrusion techniques such as injection molding, blow molding, compression molding, or extrusion of pipes, tubes, profiles, cables or films may be used with compositions of the present invention to form molded or extruded articles.
Injection molding of thermoplastics is a multi-step process by which a composition of the present invention is heated until it is molten, then forced into a closed mold where it is shaped, and finally solidified by cooling. The PHA copolymers and any optional ingredients are melt processed at melting temperatures less than about 180xc2x0 C., more typically less than about 160xc2x0 C. to minimize unwanted thermal degradation. Three common types of machines that are used in injection molding are ram, screw plasticator with injection, and reciprocating screw devices (see Encyclopedia of Polymer Science and Engineering, Vol. 8, pp. 102-138, John Wiley and Sons, New York, 1987 (xe2x80x9cEPSE-3xe2x80x9d). A ram injection molding machine is composed of a cylinder, spreader, and plunger. The plunger forces the melt in the mold. A screw plasticator with a second stage injection consists of a plasticator, directional valve, a cylinder without a spreader, and a ram. After plastication by the screw, the ram forces the melt into the mold. A reciprocating screw injection machine is composed of a barrel and a screw. The screw rotates to melt and mix the material and then moves forward to force the melt into the mold.
An example of a suitable injection molding machine is the Engel Tiebarless ES 60 TL apparatus having a mold, a nozzle, and a barrel that is divided into zones wherein each zone is equipped with thermocouples and temperature-control units. The zones of the injection molding machine can be described as front, center, and rear zones whereby the pellets are introduced into the front zone under controlled temperature. The temperature of the nozzle, mold, and barrel components of the injection molding machine can vary according to the melt processing temperature of the pellets and the molds used, but will typically be in the following ranges: nozzle, 120-170xc2x0 C.; front zone, 100-160xc2x0 C.; center zone 100-160xc2x0 C.; rear zone 60-150xc2x0 C.; and mold, 5-50xc2x0 C. Other typical processing conditions include an injection pressure of from about 2100 kPa to about 13,790 kPa, a holding pressure of about 2800 kPa to about 11,030 kPa, a hold time of about 2 seconds to about 15 seconds, and an injection speed of from about 2 cm/sec. to about 20 cm/sec. Examples of other suitable injection molding machines include Van Dorn Model 150-RS-8F, Battenfeld Model 1600, and Engel Model ES80.
Compression molding in thermoplastics consists of charging a quantity of a composition of the present invention in the lower half of an open die. The top and bottom halves of the die are brought together under pressure, and then the molten composition conforms to the shape of the die. The mold is then cooled to harden the plastic (see EPSE-3).
Blow molding is used for producing bottles and other hollow objects (see EPSE-3). In this process, a tube of molten composition known as a parison is extruded into a closed, hollow mold. The parison is then expanded by a gas, thrusting the composition against the walls of a mold. Subsequent cooling hardens the plastic. The mold is then opened and the article removed.
Blow molding has a number of advantages over injection molding. The pressures used are much lower than injection molding. Blow molding can be typically accomplished at pressures of about 170 kPa to about 690 kPa between the plastic and the mold surface. By comparison, injection molding pressures can reach about 69,000 kPa to about 137,900 kPa (see EPSE-3). In cases where the composition has a molecular weight too high for easy flow through molds, blow molding is the technique of choice. High molecular weight polymers (or copolymers) often have better properties than low molecular weight polymers, for example high molecular weight materials have greater resistance to environmental stress cracking. (see EPSE-3). It is possible to make extremely thin walls in products with blow molding. This means less composition is used, and solidification times are shorter, resulting in lower costs through material conservation and higher throughput. Another important feature of blow molding is that since it uses only a female mold, slight changes in extrusion conditions at the parison nozzle can vary wall thickness (see EPSE-3). This is an advantage with structures whose necessary wall thicknesses cannot be predicted in advance. Evaluation of articles of several thicknesses can be undertaken, and the thinnest, thus lightest and cheapest, article that meets specifications can be used.
Extrusion is used to form extruded articles, such as pipes, tubes, rods, cables, or profile shapes. Compositions are fed into a heating chamber and moved through the chamber by a continuously revolving screw. Single screw or twin screw extruders are commonly used for plastic extrusion. The composition is plasticated and conveyed through a pipe die head. A haul-off draws the pipe through the calibration and cooling section with a calibration die, a vacuum tank calibration unit and a cooling unit. Rigid pipes are cut to length while flexible pipes are wound. Profile extrusion may be carried out in a one step process. Extrusion procedures are further described in Hensen, F., Plastic Extrusion Technology, p 43-100.
Flushable tampon applicators of the present invention are molded or extruded in a desired shape or configuration using a variety of molding or extrusion techniques to provide a thermoplastic applicator comprising an outer tubular member and an inner tubular member or plunger. In another embodiment, the outer tubular member and plunger may be made by different molding or extrusion techniques, and in a further embodiment, the outer member is molded or extruded from a composition of the present invention and the plunger is made from another environmentally degradable material.
Generally, the process of making flushable tampon applicators of the present invention involves charging a composition of the present invention into a compounder, and the composition is melt blended and processed to pellets. The pellets are then constructed into flushable tampon applicators using an injection molding apparatus. The injection molding process is typically carried out under controlled temperature, time, and speed and involves melt processing pellets or thermoplastic compositions wherein the melted thermoplastic composition is injected into a mold, cooled, and molded into a desired plastic object. Alternatively, the composition can be charged directly into an injection molding apparatus and the melt molded into the desired flushable tampon applicator.
One example of a procedure of making flushable tampon applicators of the present invention involves extruding the composition at a temperature above the melting temperature of the composition to form a rod, chopping the rod into pellets, and injection molding the pellets into the desired flushable tampon applicator form.
The compounders that are commonly used to melt blend thermoplastic compositions are generally single-screw extruders, twin-screw extruders, and kneader extruders. Examples of commercially available extruders suitable for use herein include the Black-Clawson single-screw extruders, the Werner and Pfleiderer co-rotating twin-screw extruders, the HAAKE(copyright) Polylab System counter-rotating twin screw extruders, and the Buss kneader extruders. General discussions of polymer compounding and extrusion molding are disclosed in the Encyclopedia of Polymer Science and Engineering, Vol. 6, pp. 571-631, 1986, and Vol. 11, pp. 262-285, 1988; John Wiley and Sons, New York.
The flushable tampon applicators of the present invention can be packaged in any suitable wrapper provided that the wrapper is soil proof and disposable with dry waste. Wrappers made from biodegradable materials that create minimal or no environmental concerns for their disposal are an embodiment of a wrapper. It is contemplated, however, that the tampon applicators of the present invention can be packaged in flushable wrappers made from paper, nonwoven, cellulose, thermoplastic, or any other suitable flushable material, or combinations of these materials.
The molded or extruded articles produced in the present invention are environmentally degradable. xe2x80x9cEnvironmentally degradablexe2x80x9d is defined as being biodegradable, disintegratable, dispersible, or compostable or a combination thereof. xe2x80x9cFlushablexe2x80x9d as used herein means that an article can be safely flushed into a sewer system without detrimental consequences to existing sewage infrastructure systems. As a result, molded or extruded articles of the present invention can be easily and safely disposed of in solid waste composting or wastewater collection and treatment systems. The environmental degradability of the molded or extruded articles of the present invention offers a solution to the problem of accumulation of such materials in the environment following their use. The flushability of the molded or extruded articles of the present invention when used in disposable products, such as tampon applicators, offer additional convenience and discreteness to the consumer. Although biodegradability, disintegratability, dispersibility, compostibility, and flushability all have different criteria and are measured through different tests, generally the molded or extruded articles of the present invention will meet more than one of these criteria.
Biodegradable is defined as when an organic material is exposed to aerobic conditions, the material will break down into simple compounds such as carbon dioxide and water or, under anaerobic conditions, the material will break down into simple compounds such as carbon dioxide, water, and methane by the action of natural occurring microorganisms. Biodegradability means that the organic constituents of the molded or extruded articles are subject to decomposition via biological activity and there is an absence of persistent metabolites.
A variety of different standardized biodegradability methods have been established by various organizations and in different countries. For example, for aerobic biodegradability, the American Society for Testing and Materials (ASTM) has established ASTM D 5338 (Standard Test Method for the Determining Aerobic Biodegradation of Plastic Materials Under Controlled Composting Conditions) for municipal solid waste composting, and ASTM D 5271 (Standard Test Method for Assessing the Aerobic Biodegradation of Plastic Materials in an Activated Sludge Wastewater Treatment System) for municipal wastewater treatment. These tests measure the percent of test material that mineralizes as a function of time by monitoring the amount of carbon dioxide being released as a result of assimilation by microorganisms in the matrix of interest The carbon dioxide production in these tests is typically measured via electrolytic respirometry. Other standard protocols, such 301 B from the Organization for Economic Cooperation and Development (OECD), may also be used to assess the aerobic biodegradability of a material. Standard biodegradation tests in the absence of oxygen are described in various protocols such as ASTM D 5511 (Standard Test Method for Determining the Anaerobic Biodegradation of Plastic Materials Under High Solids Anaerobic Digestion Conditions) or ASTM D 5526 (Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under Accelerated Landfill Conditions). These tests are used to assess the biodegradability of materials in septic tanks, anaerobic digestion or sanitary landfills.
Disintegration is when the molded or extruded article has the ability to break up into smaller pieces by physical, chemical or biological means. Disintegration is assessed by determining the weight loss of a material under specific environmental conditions. Both aerobic and anaerobic disintegration tests are used. In these tests the weight loss is typically determined by the amount of test material that is no longer retained on an 18 mesh sieve with 1 millimeter openings after exposure to activated or digester sludge. The difference in weight between the initial sample and the sample recovered on a screen is used to determine the rate and extent of disintegration. The testing for biodegradability and disintegration are similar since essentially the same environment is used for testing. The major difference is that the weight of the material remaining is measured for disintegration, while the evolved gases are measured for biodegradation.
Molded or extruded articles of the present invention have a greater than 50% disintegration within 28 days under anaerobic conditions and, in further embodiments, greater than 60%, or greater than 80% disintegration in 28 days under such conditions.